allow setting event loop policy #4184
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can be an import string to a class or an instantiated policy
| from zmq.eventloop import ioloop | ||
| ioloop.install() | ||
| else: | ||
| ioloop = None |
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I'd be inclined to put the from tornado import here directly, so you can see both cases in one snippet.
| policy = change.new | ||
| if isinstance(policy, str): | ||
| # if it's a str, it should be an import string | ||
| policy = import_item(policy)() |
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Doesn't the Type traitlet allow importable strings already? Are there cases where it's important to pass an instance so you can instantiate it with non-default arguments?
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More importantly, is this actually useful? The problem motivating it in #4183 isn't really solved by making it configurable - as you point out, extensions are loaded too late to influence creating the event loop. @mrocklin has a workaround for dask (dask/distributed#2343), and I'm not aware of anyone else who has asked for this. How the event loop is created seems like squarely an application concern, so I'm -1 on making it configurable unless there's a clear use case that's not better solved another way. The more bits that can be configured, the harder it is to change the underlying code later. |
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While putting this together, I did realize that asyncio.set_event_loop_policy(Policy())Which isn't really any more complex than c.NotebookApp.event_loop_policy = Policy()The main difference would be that having it in config makes it explicit that users can set the event loop policy, while the other just happens to work. I think we should allow users to request running with uvloop, etc. |
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Closing this one as stale, cheers! |
can be an import string to a class or an instantiated policy
additionally, avoid calling deprecated ioloop.install with pyzmq 17. This can complicate tornado eventloop instantiation.
closes #4183 as best I can think of, since I don't think we can in general load server extensions early enough that they could do this themselves.